Currently the money makers are:
Also know as free-to-play or Asian model (as it was first introduced in Korea). Concept is very simple, full version game has to be free to play, but some items are available only through in-game purchase. EA, being currently the biggest game developer, embraced the concept and called it Play4Free. It's estimated market of in-game objects is of a few billion dollars. This model is popular with multi-player games, which are not MMOs.
Unlike above, where full version is free, in freemium one only get's basic version for free, without full capabilities. You either buy full version or pay subscription fee, to have full version. It's still quite popular with MMOs or simple Flash/HTML5 games.
Selling players profile to advertisers
Unfortunately even though it's doubtful from moral and legal point of view, still this is how many social games make their money.